Generally, conveyor systems comprise a conveyor chain or belt which moves in a generally circuitous loop, having a carrying way to support the chain or belt and a return way to support the chain or belt on its return run. The chain or belt is often made of steel or plastic, and travels in the circuitous loop about two or more sprockets, and is driven by a drive sprocket having teeth. The chain typically is adapted to flex generally in a primary direction, and to back flex in the reverse direction, although the chain typically flexes to a greater degree in the primary direction than in the reverse direction.
As the chain or belt moves along the circuitous loop, a catenary sag is provided for proper chain tension. Because conveyor chains or belts may become disengaged from the drive sprocket by excessive creeping, many chain manufacturers recommend that the chain or belt never be run tight. Thus, some sag immediately underneath the drive sprocket is normally required. The catenary sag, however, must be limited so that the entire bottom run of the chain or belt does not sag.
To limit the amount of catenary sag, standard conveyor systems comprise a return way on the bottom run of the chain or belt, which supports the chain or belt along the return run of the circuitous loop. Return ways are often comprised of wear strips which are positioned in a serpentine manner, upon which the chain or belt slides. The transition area between the catenary sag and the return way requires a guide shoe which facilitates the flexing of the chain from the primary flex to the backward flex as it moves from the front sprocket to the return way.
In the past, various types of return way guide shoes have been provided which facilitate the chain or belt's movement from the catenary sag to the return way, including a roller in combination with several other rollers comprising the return way. The problem with rollers, however, is that the rollers tended to stop rolling when they became dirty, which impeded movement of the chain, or were prone to wear out quickly.
Low friction return way guide shoes have also been provided in the past, having metal structures with plastic covers, which form the wear surface upon which the chain or belt slides. However, these guide shoes are relatively expensive to manufacture and replace, especially in view of the varying sizes and dimensions that are needed for different applications.
Recently, a return way guide shoe having a wear surface made of ultra high molecular weight polyethylene has been provided. Ultra high molecular weight polyethylene is ideally suited for this application, as it is chemical resistant, very durable, low in friction, and has high impact resistance. Though the previous return way guide shoes are useful and have many advantages, the problem is that they consisted of two separate wear surfaces, one supporting either side of the chain or belt, which tended to wear the chains or belts, particularly the plastic ones, relatively unevenly. Other guide shoes having two wear surfaces on either side have been produced in Europe in smaller sizes, but have the same problem of causing uneven wear on plastic belts or chains.
There is, therefore, a need for a guide shoe having a wear surface which extends the entire width of the chain or belt, which does not wear the plastic chains or belts unevenly. Also, there is a need for a more cost-effective return way guide shoe utilizing a material that is chemically resistant, durable, low in friction, and has high impact resistance, such as ultra high molecular weight polyethylene.